Pump intake grates- thinking of trying something taboo

[gmtech16450yz]

Ok since I can't leave anything alone and I have this insane desire to make every mechanical assembly better than it was originally designed, I'm thinking of trying the unthinkable. lol.

I'm going to remove the intake grates on my brand new boat I've had in the water 3 times now. haha. I'm going to machine blocks of aluminum to bolt into the spaces the intake grates leave so that there's absolutely no bumps or voids in the flow to the pumps. Basically it will be the same as if I cut the bars off the stock grates and just left the mounting blocks. (The grates cost about $60 each so actually just chopping the bars off the ones in my boat and ordering new ones in case it doesn't work wouldn't be that big of a deal. I wouldn't even have to take them off to do that.)

So why would I do something so seemingly stupid you ask? Because I like to learn. Yes, I FULLY understand that there is an increased risk of sucking small animals and tree stumps into my jets, but honestly how much do the stock grates cut down on those possibilities anyway? There are only two bars on these grates, they're pretty much wide open actually. You could easily suck up big enough stuff to wipe out an impeller anyway. So I don't believe the stock grates are really cutting down those chances very much over not having any at all. They certainly aren't going to stop or reduce the chances of sucking up a rope. And it can be argued that there's more chance of the sucked up rope breaking the grate and having it sucked up too, vs. not having a grate in the first place. And as far as human safety, if you're stupid enough to have your body ANYWHERE NEAR the intake of a running jet boat, you probably deserve to have your arm swallowed up and spit out. Is having no grates on a jet pump intake more dangerous than a standard prop? Oh hell no!

Seaweed- Ok I've already had so much seaweed stuffed into the grates on my boat that I had to spend 15 minutes cutting it out of the grates with a knife. You can easily reach all the way down to the grates through the cleanouts, but it's damn near impossible to push the seaweed back through the grates when it's wrapped around them. What happens in those situations when there's no grate at all? I'm thinking it would be 1000 times easier to simply push the seaweed back out of the intake, that is if it doesn't already fall out by doing the reverse trick. So for seaweed ingestion and removal, I'm thinking it's got to be better. The grates certainly aren't keeping the seaweed out of the impeller, and not having grates isn't going to change that much. Maybe if it has a nice smooth path into and through the pump it might be able to eat more seaweed without getting plugged up even.

Performance- Yeah, I'm always looking to get my equipment running at it's top efficiency, whatever it is. Will not having a grate in the intake help pump loading? I would certainly think so. As far as the physics of it, I don't believe anything in front of any kind of pump wouldn't end up being a restriction of some sort. The only exception to that might be something that directs the flow into the pump more efficiently because of design limitations of the application.

That brings me to the "Top Loader" question, has anyone tried it? I understand the idea of a vane or wing that directs water upwards into the pump. But if done wrong, it can obviously be a huge drag on the bottom of the boat. It seems that the top loader theory is more for slower speed cavitation and it doesn't do much for top speed. (I'm more interested in top speed or higher cruising speeds than out of the hole acceleration.) If I'm bored and have the time, I may make up a wing or vane to weld onto the stock grates to see if I can make a top loader myself. I don't think there's any aftermarket grates for these boats and obviously two watercraft grates, even if they bolted up, wouldn't work on a twin engine boat.

I also think boats are way different than watercraft simply because of the angle of the bow when accelerating. When you're plowing or getting out of the hole, the jet intakes are more "open" to the incoming water. When you're up on plane, the intake openings are much flatter to the water. Have you guys noticed that putting more weight in the front of these boats slows them down? On most prop boats, (in general) you want to get your passenger or cargo weight towards the front of the boat to help it plane flatter. I've already seen on my boat that too much weight at the front of the boat slows it down a lot. Is this because you're getting less pump loading? I have a feeling it is. Lowering the front of the boat puts the pump intake flatter to the water instead of letting it "scoop" a little bit. Too much "scoop" of course would slow you down though. Hmmm. so much to think about!

Sooooo, I haven't done any chopping yet, but I'm gonna lay under my boat today and stare at those grates for awhile! If anyone has ANY info or experience with any of this, let me know. Like I said, worst case is I have to buy a couple of stock grates to put back in it if I chop up the ones I have. Or also worst case- if I suck up something that destroys an impeller, I'll just end up looking into aftermarket impellers or changing pitches anyway. I just don't think there's much difference between the stock grate or no grate in being able to suck up something that can damage an impeller. Devil hates a coward!!! haha.

20170925_184235

• gmtech16450yz
• Oct 4, 2017

20170925_184153

• gmtech16450yz
• Oct 4, 2017

 

[Bluewater272]

"Is having no grates on a jet pump intake more dangerous than a standard prop? Oh hell no!"

As unlikely as it may be - if someone got their arm sucked into a jet, they might lose it AND drown as they are stuck under the boat with their mangled arm. Prop wouldn't do that necessarily. Just my two cents. I'm actually wondering why the grate couldn't be a little more substantial to prevent even smaller items from going through.

 

[Betik]

I was thinking to do the exact opposite for going through the Erie canal.
Please keep us posted. I love experiments done on other boats and I get to learn for free LOL

 

[swatski]

Ok since I can't leave anything alone and I have this insane desire to make every mechanical assembly better than it was originally designed, I'm thinking of trying the unthinkable. lol.

I'm going to remove the intake grates on my brand new boat I've had in the water 3 times now. haha. I'm going to machine blocks of aluminum to bolt into the spaces the intake grates leave so that there's absolutely no bumps or voids in the flow to the pumps. Basically it will be the same as if I cut the bars off the stock grates and just left the mounting blocks. (The grates cost about $60 each so actually just chopping the bars off the ones in my boat and ordering new ones in case it doesn't work wouldn't be that big of a deal. I wouldn't even have to take them off to do that.)

So why would I do something so seemingly stupid you ask? Because I like to learn. Yes, I FULLY understand that there is an increased risk of sucking small animals and tree stumps into my jets, but honestly how much do the stock grates cut down on those possibilities anyway? There are only two bars on these grates, they're pretty much wide open actually. You could easily suck up big enough stuff to wipe out an impeller anyway. So I don't believe the stock grates are really cutting down those chances very much over not having any at all. They certainly aren't going to stop or reduce the chances of sucking up a rope. And it can be argued that there's more chance of the sucked up rope breaking the grate and having it sucked up too, vs. not having a grate in the first place. And as far as human safety, if you're stupid enough to have your body ANYWHERE NEAR the intake of a running jet boat, you probably deserve to have your arm swallowed up and spit out. Is having no grates on a jet pump intake more dangerous than a standard prop? Oh hell no!

Seaweed- Ok I've already had so much seaweed stuffed into the grates on my boat that I had to spend 15 minutes cutting it out of the grates with a knife. You can easily reach all the way down to the grates through the cleanouts, but it's damn near impossible to push the seaweed back through the grates when it's wrapped around them. What happens in those situations when there's no grate at all? I'm thinking it would be 1000 times easier to simply push the seaweed back out of the intake, that is if it doesn't already fall out by doing the reverse trick. So for seaweed ingestion and removal, I'm thinking it's got to be better. The grates certainly aren't keeping the seaweed out of the impeller, and not having grates isn't going to change that much. Maybe if it has a nice smooth path into and through the pump it might be able to eat more seaweed without getting plugged up even.

Performance- Yeah, I'm always looking to get my equipment running at it's top efficiency, whatever it is. Will not having a grate in the intake help pump loading? I would certainly think so. As far as the physics of it, I don't believe anything in front of any kind of pump wouldn't end up being a restriction of some sort. The only exception to that might be something that directs the flow into the pump more efficiently because of design limitations of the application.

That brings me to the "Top Loader" question, has anyone tried it? I understand the idea of a vane or wing that directs water upwards into the pump. But if done wrong, it can obviously be a huge drag on the bottom of the boat. It seems that the top loader theory is more for slower speed cavitation and it doesn't do much for top speed. (I'm more interested in top speed or higher cruising speeds than out of the hole acceleration.) If I'm bored and have the time, I may make up a wing or vane to weld onto the stock grates to see if I can make a top loader myself. I don't think there's any aftermarket grates for these boats and obviously two watercraft grates, even if they bolted up, wouldn't work on a twin engine boat.

I also think boats are way different than watercraft simply because of the angle of the bow when accelerating. When you're plowing or getting out of the hole, the jet intakes are more "open" to the incoming water. When you're up on plane, the intake openings are much flatter to the water. Have you guys noticed that putting more weight in the front of these boats slows them down? On most prop boats, (in general) you want to get your passenger or cargo weight towards the front of the boat to help it plane flatter. I've already seen on my boat that too much weight at the front of the boat slows it down a lot. Is this because you're getting less pump loading? I have a feeling it is. Lowering the front of the boat puts the pump intake flatter to the water instead of letting it "scoop" a little bit. Too much "scoop" of course would slow you down though. Hmmm. so much to think about!

Sooooo, I haven't done any chopping yet, but I'm gonna lay under my boat today and stare at those grates for awhile! If anyone has ANY info or experience with any of this, let me know. Like I said, worst case is I have to buy a couple of stock grates to put back in it if I chop up the ones I have. Or also worst case- if I suck up something that destroys an impeller, I'll just end up looking into aftermarket impellers or changing pitches anyway. I just don't think there's much difference between the stock grate or no grate in being able to suck up something that can damage an impeller. Devil hates a coward!!! haha.

20170925_184235

• gmtech16450yz
• Oct 4, 2017

20170925_184153

• gmtech16450yz
• Oct 4, 2017

Very interesting! One thing I've learned with these boats - you almost never know what you going to get, until you try and test it out.
I would not be concerned about safety too much, you can still stick your arm through the grates etc.
Keeping large-er objects from getting sucked in - yes, that is a bit of a concern, you would not believe what kind of stuff has been found stuck in those intake grates! I would be more concerned about cracking the intake tunnel if something large got in there and could quite pass through, say... a tire. LOL, I think @buckbuck actually found one that way.

As far as intake and speed - not sure how much to would help, but could NOT hurt.
The bow down attitude speed reduction is notable, but that is likely due to more hull contact with water, not the intake angle.
Jet skis can benefit from top loader, but in the boats I'm not aware of any evidence of it due to larger displacement. But again - not many tried. If I were to mess with the intakes, I would probably try a top loader before anything else.

Oh, and here is what I recently "found" in my river, lol - obviously the grates did not stop that sucker. But I do think the grates must have slowed the speed of this thing passing through the tunnel, as there was no damage to anything but the impeller.



EDIT: What about that ECU reflash though????
I am itching to do it, I don't like the power/throttle curve in these boats at all, there is a lot of dead-range. It does not bother me when I use RideSteady but there is much room for improvement.
--

 

[Ronnie]

I have not found any aftermarket intake grates with a top loader design maybe the ones from the skis will work but i dont think so, not without modifications to the mounting points anyway.

In my opinion the boat slowing down as more weight is shifted to the bow is a result of more of the hull being in the water and had nothing to do with the changes in the way water is being taken in sonce the intakes are still in and surrounded by water when the bow is low.

Intererestingly, on the mercury sport jets/pumps, the standard intake grate is a 7 tine. They also offer a rock grate to keep finer material from entering the pump, the rock grate had 13 tines. The spacing between the times is less than a quarter inch on the rock grate and a half inch on the standard grate. Seadoo used to offer a surge grate with 4 tines/forks that were hinged on the leading edge with the isea being that seaweed/vegetation would pass through the grate and be mulched and spit out by the impeller. Eventually sesdoo moved away form mercury hardware and many people have complained online the surge grate let in roxks the size of baseballs. I ended up buying a rock grate for mine because the spacing of the tines would not physically allow a tow line through them.

I wish you luck on your experiments bit dont think running without intake grates will noticably improve performance. Another option to modifying grates is to remove them and fill in the mounting holes / edges with something from a 3d printer.

 

[Jgorm]

Many many years ago they used to put scoops on jet skis with no bars.

 

[Cobra Jet Steering LLC]

Ok good luck. I designed some custom intake grates that deal with the weeds for the most part so that certainly can be accomplished but if you read about the reverse move your weed situation should be a lot less stressful and annoying. Many years ago Johnny O from the other site told me that once I told him how to do the reverse move he never had to pull his cleanout plugs and he boated where I do in Tampa bay where all the weeds of the UNIVERSE originate. So that is saying something.

 

[Ilmmct]

@gmtech16450yz ... applaud the desire to learn and the ingenuity to improve upon the design.

Sorry to meddle w/metal ....

One perspective to add to your thought process ... when I sucked up an anchor rope (left in the ICW by another boater not mine) when my son-in-law was waterskiing, the current intake grate design was "helpful" in an obsure way.

The very easy to hear clank of metal as the anchor that was attached to this rope got yanked towards the impeller housing caused me to stop the boat immediately. Kind of like when someone drops a coin in a crowded room. This metal sound stopped me in my tracks, so I did not cause anymore damage to my boat.

So as you lay down there to have a look and contemplate a future design ... consider the value of metal as the proverbial canary in the coal mine. I think a "thud" (say caused by this anchor hitting fiberglass w/out the grate) might have been ignored but, this "clank" caused by the metal design was a early warning that is a collateral benefit of Yamaha's design.

 

[gmtech16450yz]

Thanks for the replies and ideas guys! I didn't do any chopping or cutting yet, but I did order an extra set of grates.

I think what I'm going to try first is actually welding in a "wing" in the center of the grates, maybe against or replacing the bar between the two rails. I'll try the top loader idea first. If it fails, then I'll try cutting the rails completely off and just mounting the ends into the boat. If THAT fails, then I'll just put the set of unmodified stock grates back in and be done with it.

Ronnie, Hey you're an SF Bay Area guy too! I actually thought about the 3d printer idea too, that's a good idea. My son works with cad/cam stuff and he could print me the pieces if I wanted. I like working with aluminum though, and it would be stronger too. Simply cutting up a stock set would be easier still though, which is probably what I'll do.

As far as my goal in all of this, I'm actually leaning more towards easy seaweed removal or lessening the chances of getting it plugged up anyway. I seriously had a TON of seaweed wrapped around the grates, there's no way it was going to come off doing the reverse trick, which I tried a few times. I still like the idea of not having anything in that intake opening. There's not much chance of seaweed getting stuck when all that's there are nice smooth sides of the giant opening in front of the shaft and impeller.

 

[Ronnie]

I hear you @gmtech16450yz , I assume you are going to experiment on what's installed already and save the new grates just in case you need them, actually I just noticed you have a 2017 model so those grates at new as well.

I also understand the weed comment and agree it would fall out a lot easier without a grate but it won't help in those situations where the vegetation is long, enters the intake and goes into or through the pump. I've had they happen a couple times, in that situation the reverse trick won't do it, had to use the clean out plugs or get in the water and do it the old fashion way.

Here is some video of me clearing the pumps in the delta near Tracy marina. This was not even the worst it's been. Two tips about the clean outs: 1. Try to use them in a no wake zone if possible/put an anchor out to keep you in the no wake zone if necessary. 2. If you are going to check one check them both.

Where do you boat at? Maybe we could hook up on the water, uh next season, unless we have another hot weekend but I think last weekend may be the swan song for this boating season.

 

[swatski]

Thanks for the replies and ideas guys! I didn't do any chopping or cutting yet, but I did order an extra set of grates.

I think what I'm going to try first is actually welding in a "wing" in the center of the grates, maybe against or replacing the bar between the two rails. I'll try the top loader idea first. If it fails, then I'll try cutting the rails completely off and just mounting the ends into the boat. If THAT fails, then I'll just put the set of unmodified stock grates back in and be done with it.

Ronnie, Hey you're an SF Bay Area guy too! I actually thought about the 3d printer idea too, that's a good idea. My son works with cad/cam stuff and he could print me the pieces if I wanted. I like working with aluminum though, and it would be stronger too. Simply cutting up a stock set would be easier still though, which is probably what I'll do.

As far as my goal in all of this, I'm actually leaning more towards easy seaweed removal or lessening the chances of getting it plugged up anyway. I seriously had a TON of seaweed wrapped around the grates, there's no way it was going to come off doing the reverse trick, which I tried a few times. I still like the idea of not having anything in that intake opening. There's not much chance of seaweed getting stuck when all that's there are nice smooth sides of the giant opening in front of the shaft and impeller.

I'm certainly watching! Any performance gains due to intake grate modifications and/or removal would be of great interest especially to the wake surfing crowd. Right now, depending on fore-aft distribution, the 240s seem to max out at about 3,000lbs of ballast (and can no longer pop up on plane). In that scenario, insufficient pump loading (and cavitation/ventilation) can in fact be an issue (or a limiting factor) it seems.

Too efficient pump loading can be disastrous in skis as at high speeds they can suffer "stuffing" the pump and lose the grip to water. No a problem with boats though! And I am a lot more interested in mods for low end pulling power/ability to haul ballast.

One thing to keep in mind is - those grate bolts are through-hull so if removed the holes may need to be (at least temporarily) plugged with silicone to prevent water intrusion and - more importantly - sucking air from the bilge (performance loss).

--

 

[1WetBoat]

Just chiming in here, but from my years with wave-runners I was under the impression that the bars on the intake grate also help the craft track straight at higher speeds. Similar to the sponsons when lower in the water. One summer i was riding in a area that can be pretty shallow, Stiltsville for those who are local, and i ran over a branch that was just under the surface. It snapped off both my bars and just left the front and rear intake grate sections bolted on. I was able to ride it back but it didn't feel as planted without the bars. Might not apply to jetboats though, but thought I should mention it.

 

[gmtech16450yz]

Just chiming in here, but from my years with wave-runners I was under the impression that the bars on the intake grate also help the craft track straight at higher speeds. Similar to the sponsons when lower in the water. One summer i was riding in a area that can be pretty shallow, Stiltsville for those who are local, and i ran over a branch that was just under the surface. It snapped off both my bars and just left the front and rear intake grate sections bolted on. I was able to ride it back but it didn't feel as planted without the bars. Might not apply to jetboats though, but thought I should mention it.

Good point, that very well could be true on the boats too. The bars are tilted so they're vertical so I guess they could aid somewhat in stability. I actually thought that if I removed them altogether that I might lose a little efficiency in a turn when the water is hitting the hull and intakes a little sideways. With the grate bars on there, there's a chance they're actually directing the water into the pump when hit from the side. ??? lol.

I'm leaning more towards keeping them but making a toploader wing. The other thing I thought about when I was under the boat staring up at the inlets is they're pretty big. My thought was maybe the fact that the physical area of the openings being somewhat large means that the grates as a restriction isn't that big of a deal but the grates being used to direct the flow into the impeller is more of a big deal. If you look at the old Berkeley jet intakes they're what I would call super restricted with grates that have bars and flow deflectors. So it would seem that the guys engineering and modding those old pumps concentrated more on tuning the flow with the grates rather than simply removing them in an attempt to eliminate restrictions.

 

[swatski]

@gmtech16450yz I curious if you would be willing to tell us more about your aluminum mill - the pics of your dashboard mods are fantastic!
I might personally like the look of matte aluminum finish more, I think, but your setup rocks.

--

 

[Jgorm]

Check these out
http://www.berkeleyjet.com/c-648-loader-scoops.aspx
https://www.watcon.com/intake-scoop-grates-r-and-d

 

[Gym]

I'm wondering if the tapered shape of the bars provide a venturi effect increasing the velocity of the water entering the tunnel. The bars could also start the water spinning in the correct direction to help reduce the load on the impeller. I will have to look closer to see if there is a camber or relative angle of attack built into the bars. Good subject though.

 

[1WetBoat]

Another thing to consider is that when you add top loader wings on the grate, it actually increases the surface area on the water and can actually scrub some speed. Usually top loaders grates are for low end while sacrificing some top speed.

 

[gmtech16450yz]

@gmtech16450yz I curious if you would be willing to tell us more about your aluminum mill - the pics of your dashboard mods are fantastic!
I might personally like the look of matte aluminum finish more, I think, but your setup rocks.

--

Thanks!
It's a Bridgeport Mill, and I LOVE it! One of my favorite pieces of equipment in my shop. Bridgeports were pretty much the gold standard in mills for decades. The design came about in the 30's and didn't change a whole lot since then. It's an amazing machine. I also have a South Bend lathe, another old American iron machine that just works. The mill was built in the '70's and the lathe I think was built in '82, one of the last ones made. I bought them both used, completely disassembled and rebuilt both of them. I painted them gloss black since the usual industrial gray seemed boring.

Yeah I'm actually not thrilled with the polished dash. I tend to polish everything I make that's aluminum, so it was a natural thing to do. I also figured it would corrode less if it was polished rather than raw aluminum. That being said, when I get a chance I'm going to pull that dash piece back off and give it a brushed finish. I might have to put a coat of clear over it though if I do that.

Hopefully photophuket hasn't made it so I can't share the links to my albums...

http://s841.photobucket.com/user/j16450yz/library/Bridgeport Mill and Shop Remodel

http://s841.photobucket.com/user/j16450yz/library/South Bend Lathe Restoration

 

[swatski]

Good point, that very well could be true on the boats too. The bars are tilted so they're vertical so I guess they could aid somewhat in stability. I actually thought that if I removed them altogether that I might lose a little efficiency in a turn when the water is hitting the hull and intakes a little sideways. With the grate bars on there, there's a chance they're actually directing the water into the pump when hit from the side. ??? lol.

I'm leaning more towards keeping them but making a toploader wing. The other thing I thought about when I was under the boat staring up at the inlets is they're pretty big. My thought was maybe the fact that the physical area of the openings being somewhat large means that the grates as a restriction isn't that big of a deal but the grates being used to direct the flow into the impeller is more of a big deal. If you look at the old Berkeley jet intakes they're what I would call super restricted with grates that have bars and flow deflectors. So it would seem that the guys engineering and modding those old pumps concentrated more on tuning the flow with the grates rather than simply removing them in an attempt to eliminate restrictions.

Here is the new RIVA gate with a scoop. Someone should seriously try something like that in a boat...
http://www.greenhulk.net/forums/showthread.php?t=266650

--

 

[gmtech16450yz]

So I still haven't gotten a set of replacement grates so I didn't want to do anything crazy yet. I decided to "blueprint" what was there. I cut the crossbar out of the stock grates and knife edged the bars. I also cleaned up the intakes a bunch, there was a pretty good ledge that the water would have to go over on the bottom edge of the intakes right in front of the impellers. This picture shows the beginning of the "porting" work I did. After I smoothed out the ledge, I filled and smoothed the rest of the gaps and holes in the intakes.

The difference was absolutely noticeable! I did everything possible to try to get either engine to cavitate, they didn't. I could go full speed and crank the wheel into a hard 360 (just put the cobra jet fins on it) and come out of it without touching the throttles. A little slip, but no cavitation whatsoever. Top speed looked to be about the same, but the pumps definitely worked better at all speeds and rpm's. I have no idea if it was the minor grate mod, the minor intake tunnel smoothing or eliminating that ledge on the bottom side of the impeller opening that made it so different. Sometimes it's simply doing a whole bunch of "little" things that make something work more efficiently. In everything I do on cars, that's always been true. Attention to details makes the total package work better.

Anyway, I may still put a couple of wings or blades on those grates similar to the loader grates later. I'm just not sure I can improve on the way it's working right now. What I'm going to work on now is getting both the engines synced up a little closer power wise. I'm thinking about either making a nozzle insert for the port side or boring out the starboard side nozzle a little bit. Same as it was stock, the port engine still turns a little faster than the starboard side. I either need to put a little more load on the one, or free up the load on the other one to even them out a little more.

20171010_150659

• gmtech16450yz
• Oct 19, 2017
• 1

20171010_143037

• gmtech16450yz
• Oct 19, 2017